bug fixes for cp_wa and cg

[elainehu222]

No description provided.

[ChuanyuXue]

This pull request introduces important changes to the scheduling and constraint logic in the cg.py and cp_wa.py algorithms, aiming to improve correctness in unschedulable task detection and delay constraint calculations.

Scheduling logic improvements:

• In tsnkit/algorithms/cg.py, the solve method now checks for missing paths for each task and immediately returns an unschedulable result if any are found.

Constraint calculation corrections:

• In tsnkit/algorithms/cp_wa.py, the delay constraint calculation in add_delay_const has been updated to use the end time of the first link and the start time of the last link, ensuring more accurate enforcement of task deadlines.